Add a footer about other forms of history to the MD history page.

chrome/browser/resources/md_history/app.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 Polymer({
   is: 'history-app',
 
   properties: {
     // The id of the currently selected page.
     selectedPage_: {type: String, value: 'history', observer: 'unselectAll'},
@@ skipping 59 matching lines @@
    * Listens for history-item being selected or deselected (through checkbox)
    * and changes the view of the top toolbar.
    * @param {{detail: {countAddition: number}}} e
    */
   checkboxSelected: function(e) {
     var toolbar = /** @type {HistoryToolbarElement} */ (this.$.toolbar);
     toolbar.count += e.detail.countAddition;
   },
 
   /**
+   * @return {HistorySideBarElement} The side bar of this history app.
+   */
+  getSideBar: function() {
+    return this.$['side-bar'];
+  },
+
+  /**
    * Listens for call to cancel selection and loops through all items to set
    * checkbox to be unselected.
    * @private
    */
   unselectAll: function() {
     var listContainer =
         /** @type {HistoryListContainerElement} */ (this.$['history']);
     var toolbar = /** @type {HistoryToolbarElement} */ (this.$.toolbar);
     listContainer.unselectAllItems(toolbar.count);
     toolbar.count = 0;
@@ skipping 77 matching lines @@
    * @param {boolean} incremental
    * @param {string} searchTerm
    * @return {boolean} Whether a loading spinner should be shown (implies the
    *     backend is querying a new search term).
    * @private
    */
   shouldShowSpinner_: function(querying, incremental, searchTerm) {
     return querying && !incremental && searchTerm != '';
   },
 });